WHM Backup

I have a few questions regarding WHM's Backup option. I've never really used it, so I want to make sure I'm not messing anything up.

I have a server dedicated to one site. The site is HUGE, and has roughly 600,000 page views a day (expected to be closer to 12,000,000 within the year). It has a MySQL database tied to it that's about 4GB, and has about 500,000 text files in 60,000 directories that are used for visitors to send Private Messages, etc.

And so on. There are currently three /userpath_[X]/ directories, and the first two have 30,000 [user] directories in them (the third isn't full, but when it has 30,000 users, the system will create /userpath_4/).

Knowing that, here are my questions:

1. How reliable is WHM's backup? Would I ever run the risk of being in the middle of a backup, hitting an error (ie, high server load crashes the server), and losing everything?

2. In the configuration, I want to have a daily backup, but even in the worst case scenario, I would never want to restore anything more than a day old. Under "Backup Retention", so I uncheck Weekly and Monthly? I'm guessing that's what's meant with this section, but there's no explanation so I wasn't sure.

3. Is there a reason to NOT enable "Incremental Backup"? Generally, it sounds better to only backup what has changed that day, but not if it's significantly slower. Are there issues with this that I should know?

4. Am I correct in assuming that "Backup Accounts" would back up everything from my site? Including the Private Message folders mentioned above?

5. Assuming so, is there a reason to NOT enable "Compress Account Backups"?

6. Under "Backup SQL Databases", is there a reason to not select "Per Account and Entire MySQL Directory"? Remember, there's only one account on this server.

7. I have a second hard drive on my server named /backup/, and this is the destination for the backups (naturally). Should I list it as "/backup", or "/backup/" (note the trailing slash)?

If there's any other advice you can offer, please feel free to let me know. I might be paranoid, but the site has 8 years worth of data; if I lost any of it by running an untrustworthy program, it would have major ramifications for me.